Apparatuses and methods for dynamic targeted refresh steals

ABSTRACT

Embodiments of the disclosure are drawn to apparatuses, systems, and methods for dynamic targeted refresh steals. A memory bank may receive access commands and then periodically enter a refresh mode, where auto-refresh operations and targeted refresh operations are performed. The memory bank may receive a refresh management command based on a count of access commands directed to the memory bank. Responsive to the refresh management signal, a panic targeted refresh operation may be performed on the memory bank. A number of times the refresh management signal was issued may be counted, and based on that count a next periodic targeted refresh operation may be skipped.

BACKGROUND

This disclosure relates generally to semiconductor devices, and more specifically to semiconductor memory devices. In particular, the disclosure relates to volatile memory, such as dynamic random access memory (DRAM). Information may be stored on individual memory cells of the memory as a physical signal (e.g., a charge on a capacitive element). The memory may be a volatile memory, and the physical signal may decay over time (which may degrade or destroy the information stored in the memory cells). It may be necessary to periodically refresh the information in the memory cells by, for example, rewriting the information to restore the physical signal to an initial value.

As memory components have decreased in size, the density of memory cells has greatly increased. Repeated access to a particular memory cell or group of memory cells (often referred to as a ‘row hammer’) may cause an increased rate of data degradation in nearby memory cells. Memory cells affected by the row hammer effect may be identified and refreshed as part of a targeted refresh operation. These targeted refresh operations may take the place of (e.g., steal) time slots which would otherwise be used for a background refresh operation. It may be desirable to balance the number of background refresh operations and targeted refresh operations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a semiconductor device according an embodiment of the disclosure.

FIG. 2 is a block diagram of a refresh control circuit according to an embodiment of the present disclosure.

FIGS. 3A-3B are timing diagrams of an operation of a refresh control circuit according to an embodiment of the present disclosure.

FIG. 4 is a schematic diagram of a skip logic circuit according to an embodiment of the present disclosure.

FIG. 5 is a timing diagram of a signals of a skip logic circuit according to an embodiment of the present disclosure.

FIG. 6 is a flow chart of a method of dynamic targeted refresh steals according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

The following description of certain embodiments is merely exemplary in nature and is in no way intended to limit the scope of the disclosure or its applications or uses. In the following detailed description of embodiments of the present systems and methods, reference is made to the accompanying drawings which form a part hereof, and which are shown by way of illustration specific embodiments in which the described systems and methods may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice presently disclosed systems and methods, and it is to be understood that other embodiments may be utilized and that structural and logical changes may be made without departing from the spirit and scope of the disclosure. Moreover, for the purpose of clarity, detailed descriptions of certain features will not be discussed when they would be apparent to those with skill in the art so as not to obscure the description of embodiments of the disclosure. The following detailed description is therefore not to be taken in a limiting sense, and the scope of the disclosure is defined only by the appended claims.

Information in a volatile memory device may be stored in memory cells (e.g., as a charge on a capacitive element), and may decay over time. The memory cells may be organized into rows (wordlines) and columns (bit lines), and the memory cells may be refreshed on a row-by-row basis. In order to prevent information from being lost or corrupted due to this decay, the memory may carry out a background refresh process, such as refresh operations as part of a refresh mode. During a refresh operation, information may be rewritten to the wordline to restore its initial state. Auto-refresh operations may be performed on the wordlines of the memory in a sequence such that over time each of the wordlines of the memory are refreshed at a rate faster than the expected rate of data degradation.

Repeated access to a particular row of memory (e.g., an aggressor row) may cause an increased rate of decay in rows (e.g., victim rows) which are close to the aggressor row. These repeated accesses may be part of a deliberate attack against the memory and/or may be due to ‘natural’ access patterns of the memory. The increased rate of decay in the victim rows may require that they be refreshed as part of a targeted refresh operation. The memory device may periodically perform targeted refresh operations as part of the refresh mode. For example, when the memory device is in a refresh mode it may perform a set of refresh operations including a number of auto-refresh operations, and a number of targeted refresh operations and then repeat this cycle. In some embodiments, the targeted refresh operations may ‘steal’ timeslots which would otherwise be used for auto-refresh operations. A memory device may generally cycle between performing access operations for a period of time, entering a refresh mode for a period of time, performing access operations and so forth.

If a memory begins receiving access requests at a very high rate, it may indicate that an attack against the memory is occurring and it may be desirable to perform targeted refresh operations even when the device is not in a refresh mode. Based on rate of access commands (e.g., on a bank-by-bank basis), a targeted refresh request command (e.g., a refresh management signal) may be issued which may lead to additional targeted refresh operations being performed while the memory is not in the refresh mode (e.g., in addition to the periodic targeted refresh operations). However, as the number of targeted refresh operations between refresh modes increases, it may be less necessary to perform targeted refresh operations within the next refresh mode. It may be desirable to manage targeted refresh operations so that as the number of requested targeted refresh operations increases, less periodic targeted refresh operations are performed during the next refresh mode.

The present disclosure is drawn to apparatuses, systems, and methods for dynamic targeted refresh steals. A memory controller may count a number of access commands which are being issued to particular bank of the memory. Once the count of access commands meets or exceeds a threshold, the controller may send a refresh management signal and decrease the count. Accordingly, the memory device may receive access commands along with refresh management commands. Responsive to the refresh management signal, the memory may perform a targeted refresh operation, even if the memory is not otherwise performing refresh operations (e.g., is not currently in a refresh mode). The memory device may count a number of times a refresh management signal is issued, and may decrease a number of periodic targeted refresh operations during a next refresh mode as the count of refresh management signals increases. For example, when the count of refresh management signals meets or exceeds a threshold, a next periodic targeted refresh operation may be skipped and the count may be decreased.

FIG. 1 is a block diagram of a semiconductor device according an embodiment of the disclosure. The semiconductor device 100 may be a semiconductor memory device, such as a DRAM device integrated on a single semiconductor chip.

The semiconductor device 100 includes a memory array 118. The memory array 118 is shown as including a plurality of memory banks. In the embodiment of FIG. 1, the memory array 118 is shown as including eight memory banks BANK0-BANK7. More or fewer banks may be included in the memory array 118 of other embodiments. Each memory bank includes a plurality of word lines WL, a plurality of bit lines BL and/BL, and a plurality of memory cells MC arranged at intersections of the plurality of word lines WL and the plurality of bit lines BL and/BL. The selection of the word line WL is performed by a row decoder 108 and the selection of the bit lines BL and/BL is performed by a column decoder 110. In the embodiment of FIG. 1, the row decoder 108 includes a respective row decoder for each memory bank and the column decoder 110 includes a respective column decoder for each memory bank. The bit lines BL and/BL are coupled to a respective sense amplifier (SAMP). Read data from the bit line BL or/BL is amplified by the sense amplifier SAMP, and transferred to read/write amplifiers 120 over complementary local data lines (LIOT/B), transfer gate (TG), and complementary main data lines (MIOT/B). Conversely, write data outputted from the read/write amplifiers 120 is transferred to the sense amplifier SAMP over the complementary main data lines MIOT/B, the transfer gate TG, and the complementary local data lines LIOT/B, and written in the memory cell MC coupled to the bit line BL or/BL.

The semiconductor device 100 may employ a plurality of external terminals that include command and address (C/A) terminals coupled to a command and address bus to receive commands and addresses, and a CS signal, clock terminals to receive clocks CK and/CK, data terminals DQ to provide data, and power supply terminals to receive power supply potentials VDD, VSS, VDDQ, and VSSQ.

The clock terminals are supplied with external clocks CK and/CK that are provided to an input circuit 112. The external clocks may be complementary. The input circuit 112 generates an internal clock ICLK based on the CK and/CK clocks. The ICLK clock is provided to the command decoder 110 and to an internal clock generator 114. The internal clock generator 114 provides various internal clocks LCLK based on the ICLK clock. The LCLK clocks may be used for timing operation of various internal circuits. The internal data clocks LCLK are provided to the input/output circuit 122 to time operation of circuits included in the input/output circuit 122, for example, to data receivers to time the receipt of write data.

The C/A terminals may be supplied with memory addresses. The memory addresses supplied to the C/A terminals are transferred, via a command/address input circuit 102, to an address decoder 104. The address decoder 104 receives the address and supplies a decoded row address XADD to the row decoder 108 and supplies a decoded column address YADD to the column decoder 110. The address decoder 104 may also supply a decoded bank address BADD, which may indicate the bank of the memory array 118 containing the decoded row address XADD and column address YADD. The C/A terminals may be supplied with commands. Examples of commands include timing commands for controlling the timing of various operations, access commands for accessing the memory, such as read commands for performing read operations and write commands for performing write operations, as well as other commands and operations. The access commands may be associated with one or more row address XADD, column address YADD, and bank address BADD to indicate the memory cell(s) to be accessed.

The commands may be provided as internal command signals to a command decoder 106 via the command/address input circuit 102. The command decoder 106 includes circuits to decode the internal command signals to generate various internal signals and commands for performing operations. For example, the command decoder 106 may provide a row command signal to select a word line and a column command signal to select a bit line.

The device 100 may receive an access command which is a read command. When a read command is received, and a bank address, a row address and a column address are timely supplied with the read command, read data is read from memory cells in the memory array 118 corresponding to the row address and column address. The read command is received by the command decoder 106, which provides internal commands so that read data from the memory array 118 is provided to the read/write amplifiers 120. The read data is output to outside from the data terminals DQ via the input/output circuit 122.

The device 100 may receive an access command which is a write command. When the write command is received, and a bank address, a row address and a column address are timely supplied with the write command, write data supplied to the data terminals DQ is written to a memory cells in the memory array 118 corresponding to the row address and column address. The write command is received by the command decoder 106, which provides internal commands so that the write data is received by data receivers in the input/output circuit 122. Write clocks may also be provided to the external clock terminals for timing the receipt of the write data by the data receivers of the input/output circuit 122. The write data is supplied via the input/output circuit 122 to the read/write amplifiers 120, and by the read/write amplifiers 120 to the memory array 118 to be written into the memory cell MC.

The device 100 may also receive commands causing it to carry out one or more refresh operations as part of a self-refresh mode. The device 100 may be periodically placed in a refresh mode. Thus, refresh operations may be performed periodically each time the memory device is in the refresh mode. In some embodiments, the refresh mode command may be externally issued to the memory device 100. In some embodiments, the refresh mode command may be periodically generated by a component of the device. In some embodiments, when an external signal indicates a refresh mode entry command, the refresh signal AREF may also be activated. The refresh signal AREF may be a pulse signal which is activated when the command decoder 106 receives a signal which indicates entry to the self-refresh mode. The refresh signal AREF may be activated once immediately after command input, and thereafter may be cyclically activated at desired internal timing. The refresh signal AREF may be used to control the timing of refresh operations during the refresh mode. A self-refresh exit command may cause the automatic activation of the refresh signal AREF to stop and may cause the device 100 to return to an idle state and/or resume other operations.

The refresh signal AREF is supplied to the refresh control circuit 116. The refresh control circuit 116 supplies a refresh row address RXADD to the row decoder 108, which may refresh one or more wordlines WL indicated by the refresh row address RXADD. In some embodiments, the refresh address RXADD may represent a single wordline. In some embodiments, the refresh address RXADD may represent multiple wordlines, which may be refreshed sequentially or simultaneously by the row decoder 108. In some embodiments, the number of wordlines represented by the refresh address RXADD may vary from one refresh address to another. The refresh control circuit 116 may control a timing of the refresh operation, and may generate and provide the refresh address RXADD. The refresh control circuit 116 may be controlled to change details of the refreshing address RXADD (e.g., how the refresh address is calculated, the timing of the refresh addresses, the number of wordlines represented by the address), or may operate based on internal logic.

The refresh control circuit 116 may selectively output a targeted refresh address (e.g., which specifies one or more victim address based on an aggressor) or an automatic refresh address (e.g., from a sequence of auto-refresh addresses) as the refresh address RXADD. Based on the type of refresh address RXADD, the row decoder 108 may perform a targeted refresh or auto-refresh operation. The automatic refresh addresses may be from a sequence of addresses which are provided based on activations of the refresh signal AREF. The refresh control circuit 116 may cycle through the sequence of auto-refresh addresses at a rate determined by AREF. In some embodiments, the auto-refresh operations may generally occur with a timing such that the sequence of auto-refresh addresses is cycled such that no information is expected to degrade in the time between auto-refresh operations for a given wordline. In other words, auto-refresh operations may be performed such that each wordline is refreshed at a rate faster than the expected rate of information decay.

As used herein, an activation of a signal may refer to any portion of a signal's waveform that a circuit responds to. For example, if a circuit responds to a rising edge, then a signal switching from a low level to a high level may be an activation. One example type of activation is a pulse, where a signal switches from a low level to a high level for a period of time, and then back to the low level. This may trigger circuits which respond to rising edges, falling edges, and/or signals being at a high logical level.

The refresh control circuit 116 may also determine targeted refresh addresses which are addresses that require refreshing (e.g., victim addresses corresponding to victim rows) based on the access pattern of nearby addresses (e.g., aggressor addresses corresponding to aggressor rows) in the memory array 118. The refresh control circuit 116 may use one or more signals of the device 100 to calculate the targeted refresh address RXADD. For example, the refresh address RXADD may be a calculated based on the row addresses XADD provided by the address decoder.

In some embodiments, the refresh control circuit 116 may sample the current value of the row address XADD provided by the address decoder 104 along a row address bus, and determine a targeted refresh address based on one or more of the sampled addresses. The sampled addresses may be stored in a data storage unit of the refresh control circuit. When a row address XADD is sampled, it may be compared to the stored addresses in the data storage unit. In some embodiments, the aggressor address may be determined based on the sampled and/or stored addresses. For example, the comparison between the sampled address and the stored addresses may be used to update a count value (e.g., an access count) associated with the stored addresses and the aggressor address may be calculated based on the count values. The refresh addresses RXADD may then be used based on the aggressor addresses.

While in general the present disclosure refers to determining aggressor and victim wordlines and addresses, it should be understood that as used herein, an aggressor wordline does not necessarily need to cause data degradation in neighboring wordlines, and a victim wordline does not necessarily need to be subject to such degradation. The refresh control circuit 116 may use some criteria to judge whether an address is an aggressor address, which may capture potential aggressor addresses rather than definitively determining which addresses are causing data degradation in nearby victims. For example, the refresh control circuit 116 may determine potential aggressor addresses based on a pattern of accesses to the addresses and this criteria may include some addresses which are not aggressors, and miss some addresses which are. Similar victim addresses may be determined based on which wordlines are expected to be effected by aggressors, rather than a definitive determination of which wordlines are undergoing an increased rate of data decay.

The refresh address RXADD may be provided with a timing based on a timing of the refresh signal AREF. During the periodic refresh operations of a refresh mode, the refresh control circuit 116 may have time slots corresponding to the timing of AREF, and may provide one or more refresh addresses RXADD during each time slot. In some embodiments, the targeted refresh address may be issued in (e.g., “steal”) a time slot which would otherwise have been assigned to an auto-refresh address. In some embodiments, certain time slots may be reserved for targeted refresh addresses, and the refresh control circuit 116 may determine whether to provide a targeted refresh address, not provide an address during that time slot, or provide an auto-refresh address instead during the time slot.

The refresh control circuit 116 may use multiple methods to determine the timing of targeted refresh operations. The refresh control circuit 116 may have periodic targeted refresh operations during a refresh mode, where the refresh control circuit 116 performs auto-refresh operations and targeted refresh operations (e.g., by providing a targeted refresh address as the refresh address RXADD) based on a periodic schedule. For example, after entering a refresh mode, the refresh control circuit 116 may perform a certain number of auto-refresh operations, and then perform (e.g., steal) a certain number of targeted refresh operations.

The refresh control circuit 116 may also perform requested targeted refresh operations or panic targeted refresh operations, which may be based on access patterns to the bank associated with the refresh control circuit 116. The device 100 may receive commands which are refresh management commands (e.g., may receive request management commands at the command/address terminal C/A). The command decoder circuit 106 may provide a refresh management signal RFM based on the refresh management command. In some embodiments, the refresh management command may be the signal RFM, which may be passed directly to the refresh control circuit 116. Responsive to an activation of the RFM signal, the refresh control circuit 116 may indicate that a panic targeted refresh operation should be performed.

These panic targeted refresh operations may happen outside of a refresh period. For example, a high rate of accesses to the bank may indicate that an attack is taking place, and the refresh control circuit 116 may count the access commands and perform a panic targeted refresh operation once the count exceeds a threshold. As the number of panic targeted refresh operations increases, the refresh control circuit 116 may decrease a number of periodic targeted refresh operations during the next refresh mode. It should be understood that the process of refreshing wordlines during a periodic and panic targeted refresh operation may generally be the same, and the difference may generally be in the timing of when the refreshes are performed.

The power supply terminals are supplied with power supply potentials VDD and VSS. The power supply potentials VDD and VSS are supplied to an internal voltage generator circuit 124. The internal voltage generator circuit 124 generates various internal potentials VPP, VOD, VARY, VPERI, and the like based on the power supply potentials VDD and VSS supplied to the power supply terminals. The internal potential VPP is mainly used in the row decoder 108, the internal potentials VOD and VARY are mainly used in the sense amplifiers SAMP included in the memory array 118, and the internal potential VPERI is used in many peripheral circuit blocks.

The power supply terminals are also supplied with power supply potentials VDDQ and VSSQ. The power supply potentials VDDQ and VSSQ are supplied to the input/output circuit 122. The power supply potentials VDDQ and VSSQ supplied to the power supply terminals may be the same potentials as the power supply potentials VDD and VSS supplied to the power supply terminals in an embodiment of the disclosure. The power supply potentials VDDQ and VSSQ supplied to the power supply terminals may be different potentials from the power supply potentials VDD and VSS supplied to the power supply terminals in another embodiment of the disclosure. The power supply potentials VDDQ and VSSQ supplied to the power supply terminals are used for the input/output circuit 122 so that power supply noise generated by the input/output circuit 122 does not propagate to the other circuit blocks.

FIG. 2 is a block diagram of a refresh control circuit according to an embodiment of the present disclosure. The refresh control circuit 216 may, in some embodiments, be included in the refresh control circuit 116 of FIG. 1. Certain internal components and signals of the refresh control circuit 216 are shown to illustrate the operation of the refresh control circuit 216. The dotted line 218 is shown to represent that in certain embodiments, each of the components (e.g., the refresh control circuit 216 and row decoder 208) may correspond to a particular bank of memory, and that these components may be repeated for each of the banks of memory. Thus, there may be multiple refresh control circuits 216 and row decoders 208. For the sake of brevity, only components for a single bank will be described.

A DRAM interface 226 may provide one or more signals to an address refresh control circuit 216 and row decoder 208. The refresh control circuit 216 may include a sample timing circuit 230, an aggressor detector circuit 232, a row hammer refresh (RHR) state control circuit 236 and a refresh address generator 234. The DRAM interface 226 may provide one or more control signals, such as a refresh signal AREF, activation and pre-charge signals ACT/Pre, and a row address XADD. The refresh control circuit 216 provides refresh address RXADD with timing based on the refresh signal AREF when the bank associated with the refresh control circuit 216 is in the refresh mode. The refresh control circuit may also provide the refresh address RXADD (and other signals) to indicate a panic targeted refresh based on a pattern of accesses to the bank of the memory.

In the example embodiment of FIG. 2, the aggressor detector circuit 232 may sample the current row address XADD responsive to an activation of an optional sampling signal ArmSample provided by the sample timing circuit 230. The aggressor detector circuit 232 may be coupled to all of the row addresses XADD sent along the row address bus, but may only receive (e.g., process, pay attention to) the current value of the row address XADD when there is an activation of the sampling signal ArmSample. In other example embodiments sampling may not be used.

The received row addresses (either the sampled addresses or all addresses) may be stored in the aggressor circuit 232 and/or compared to previously stored addresses. The aggressor detector circuit 232 may provide a match address HitXADD based on a current row address XADD and/or previously stored row addresses. The RHR state control circuit 236 may provide the signal RHR to indicate that a row hammer refresh (e.g., a refresh of the victim rows corresponding to an identified aggressor row) should occur. The RHR state control circuit 236 may also provide an internal refresh signal IREF, to indicate that an auto-refresh should occur.

Responsive to an activation of RHR or IREF, the refresh address generator 234 may provide a refresh address RXADD, which may be an auto-refresh address or may be one or more victim addresses corresponding to victim rows of the aggressor row corresponding to the match address HitXADD. The RHR state control circuit 236 may provide a set of activations of RHR and IREF responsive to the refresh signal AREF. The row decoder 208 may perform a refresh operation responsive to the refresh address RXADD and the row hammer refresh signal RHR. The row decoder 208 may perform an auto-refresh operation based on the refresh address RXADD and the internal refresh signal IREF.

The DRAM interface 226 may represent one or more components which provides signals to components of the bank. In some embodiments, the DRAM interface 226 may represent a memory controller coupled to the semiconductor memory device (e.g., device 100 of FIG. 1). In some embodiments, the DRAM interface 226 may represent components such as the command address input circuit 102, the address decoder 104, and/or the command decoder 106 of FIG. 1. The DRAM interface 226 may provide a row address XADD, the refresh signal AREF, and access signals such as an activation signal ACT and a pre-charge signal Pre. Although not shown in FIG. 2, the DRAM interface 226 may also provide a bank address BADD, which may indicate which bank the accessed row address XADD is located in. The bank address BADD may activate a particular refresh control circuit 216 associated with the bank indicated by the bank address BADD. The DRAM interface may also put the refresh control circuit into a refresh mode by providing activations of the refresh signal AREF. The refresh signal AREF may be a periodic signal provided during a refresh mode which may indicate a timing for refresh operations. The access signals ACT and Pre may generally be provided as part of an access operation along with a row address XADD. The activation signal ACT may be provided to activate a given bank of the memory. The pre-charge signal Pre may be provided to pre-charge the given bank of the memory. The row address XADD may be a signal including multiple bits (which may be transmitted in series or in parallel) and may correspond to a specific row of an activated memory bank.

In the example embodiment of FIG. 2, the refresh control circuit 216 uses sampling to monitor a portion of the row addresses XADD provided along the row address bus. Accordingly, instead of responding to every row address, the refresh control circuit 216 may sample the current value of the row address XADD on the row address bus, and may determine which addresses are aggressors based on the sampled row addresses. The timing of sampling by the refresh control circuit 216 may be controlled by the sample timing circuit 230 which provides the sampling signal ArmSample. The sample timing circuit 230 may provide activations of the sampling signal ArmSample, and each activation of the signal ArmSample may indicate that a current value of the row address should be sampled. An activation of ArmSample may be a ‘pulse’, where ArmSample is raised to a high logic level and then returns to a low logic level. The activations of the signal ArmSample may be provided with periodic timing, random timing, semi-random timing, pseudo-random timing, or combinations thereof. In some embodiments, the timing of the signal ArmSample may be based, in part, on one or more other signals, such as access signals ACT/Pre. In other embodiments, sampling may not be used, and the aggressor detector circuit 232 may receive every value of the row address XADD along the row address bus. In such embodiments, the sample timing circuit 230 and the sampling signal ArmSample may be omitted.

The aggressor detector circuit 232 may receive the row address XADD from the DRAM interface 226 and the signal ArmSample from the sample timing circuit 230. The row address XADD on the row address bus may change as the DRAM interface 226 directs access operations (e.g., read and write operations) to different rows of the memory cell array (e.g., memory cell array 118 of FIG. 1). Each time the aggressor detector circuit 232 receives an activation (e.g., a pulse) of the signal ArmSample, the aggressor detector circuit 232 may sample the current value of XADD.

The aggressor detector circuit 232 may determine aggressor addresses based on one or more of the sampled row addresses, and then may provide the determined aggressor address as the match address HitXADD. The aggressor detector circuit 232 may include a data storage unit (e.g., a number of registers), which may be used to store sampled row addresses. In some example embodiments, when the aggressor detector circuit 232 samples a new value of the row address XADD (e.g., responsive to an activation of ArmSample) it may compare the sampled row address to the addresses stored in the data storage unit. If there is a match between the sampled address and one of the stored addresses, the aggressor detector circuit 232 may provide a match signal Match. In some example embodiments, the match address HitXADD may be one of the addresses stored in the aggressor detector circuit 232 which has been matched by the sampled address XADD the most frequently. For example, the aggressor detector circuit 232 may count a number of times that each address XADD is received, and provide the address which has been received the most times as the match address HitXADD.

The memory device may carry out a sequence of refresh operations in order to periodically refresh the rows of the memory device as part of a refresh mode. The RHR state control circuit 236 may determine if a given refresh operation is an auto-refresh operation or a targeted refresh operation. The RHR signal may be generated in order to indicate that the device should refresh a particular targeted row (e.g., a victim row) instead of an address from the sequence of auto-refresh addresses. The RHR state control circuit 236 may also provide an internal refresh signal IREF, which may indicate that an auto-refresh operation should take place. In some embodiments, the signals RHR and IREF may be generated such that they are not active at the same time (e.g., are not both at a high logic level at the same time). In some embodiments, IREF may be activated for every refresh operation, and an auto-refresh operation may be performed unless RHR is also active, in which case a targeted refresh operation is performed instead. The RHR state control circuit may perform a sequence of auto-refresh operations and targeted refresh operation responsive to one or more activations of the refresh signal AREF.

In some embodiments, the refresh control circuit 216 may perform multiple refresh operations responsive to each activation of the refresh signal AREF. For example, each time the refresh signal AREF is received, the refresh control circuit 216 may perform K different refresh operations, by providing K different refresh addresses RXADD. Each refresh operation may be referred to as a ‘pump’. Each of the K different refresh operations may be an auto-refresh operation or a targeted refresh operation. In some embodiments, the number of targeted and auto-refresh operations may be constant in each group of pumps responsive to an activation of the refresh signal AREF. In some embodiments it may vary.

The refresh address generator 234 may receive the row hammer refresh signal RHR and the match address HitXADD. The match address HitXADD may represent an aggressor row. The refresh address generator 234 may determine the locations of one or more victim rows based on the match address HitXADD and provide them as the refresh address RXADD when the signal RHR indicates a targeted refresh operation. In some embodiments, the victim rows may include rows which are physically adjacent to the aggressor row (e.g., HitXADD+1 and HitXADD−1). In some embodiments, the victim rows may also include rows which are physically adjacent to the physically adjacent rows of the aggressor row (e.g., HitXADD+2 and HitXADD−2). Other relationships between victim rows and the identified aggressor rows may be used in other examples. For example, +/−3, +/−4, and/or other rows may also be refreshed.

The refresh address generator 234 may determine the value of the refresh address RXADD based on the row hammer refresh signal RHR. In some embodiments, when the signal RHR is not active, the refresh address generator 234 may provide one of a sequence of auto refresh addresses. When the signal RHR is active, the refresh address generator 234 may provide a targeted refresh address, such as a victim address, as the refresh address RXADD. In some embodiments, the refresh address generator 234 may count activations of the signal RHR, and may provide closer victim rows (e.g., HitXADD+/−1) more frequently than victim rows which are further away from the aggressor address (e.g., HitXADD+/−2).

The row decoder 208 may perform one or more operations on the memory array (not shown) based on the received signals and addresses. For example, responsive to the activation signal ACT and the row address XADD (and IREF and RHR being at a low logic level), the row decoder 208 may direct one or more access operations (for example, a read operation) on the specified row address XADD. Responsive to the RHR signal being active, the row decoder 208 may refresh the refresh address RXADD.

The refresh control circuit 216 receives a refresh management signal RFM, which may be provided to a memory device (e.g., device 100 of FIG. 1) based on access operations performed on the bank associated with the refresh control circuit 216. Responsive to the signal RFM, the RHR state control circuit 236 may perform a targeted refresh operation even if the device is not otherwise performing refresh operations.

Accordingly, the RHR state control circuit 236 may indicate that targeted refresh operations should be performed as part of a periodic sequence, and may also indicate that targeted refresh operations should be performed responsive to an activation of the signal RFM. Targeted refresh operations performed as part of a periodic sequence of refresh operations may generally be referred to as ‘periodic targeted refresh operations’ in order to distinguish them from targeted refresh operations performed responsive to the signal RFM, which may generally be referred to as ‘requested targeted refresh operations’ or ‘panic targeted refresh operations’. It should be understood that the method of actually performing the periodic targeted refresh operation and the requested targeted refresh operation may generally be the same (e.g., refreshing victim wordlines based on the match address HitXADD), and the different terminology is meant to distinguish the cause of a particular targeted refresh operation.

A memory controller may monitor the access commands which are being provided to a given bank of the memory. The memory controller may include a refresh management (RFM) logic circuit which may include a count value. The count value stored in the RFM logic circuit may be a rolling accumulated ACT (RAA) count. The controller may include a separate count value RAA for each bank of the memory device and may separately compare each count value RAA to a threshold to determine if the signal RFM (or a refresh management command) should be provided to the bank associated with that count value RAA. The RAA count may be compared to a threshold which is an RAA initial management threshold (RAAIMT). The value of the threshold RAAIMT may be a configurable value.

The signal RFM may be provided to the memory device based on the comparison of the count RAA to the threshold RAAIMT. For example, in an embodiment where the count RAA is increased responsive to each activation of ACT, the controller may determine if the count RAA is greater than the threshold RAAIMT. In such an embodiment, if the count RAA is greater than RAAIMT, then the signal RFM is provided to the refresh control circuit 216. When the signal RFM is provided, the value of the count RAA may be changed. For example, if the count RAA is increased (e.g., incremented) responsive to ACT, then responsive to the signal RFM being provided, the count RAA may be decreased. In some embodiments, the count RAA may be decreased by the value of the threshold RAAINT. In some embodiments, the count value RAA may have a minimum value (e.g., 0) which the count value RAA cannot be decreased below even if the reduction of RAA by the value of RAAINT would normally be below that minimum value.

The RHR state control circuit 236 may receive the refresh signal AREF and the signal RFM and provide the row hammer refresh signal RHR and internal refresh signal IREF. The refresh signal AREF may be periodically generated and may be used to control the timing of refresh operations. The signals RHR and IREF may be used to control whether the memory performs a targeted refresh operation or an auto-refresh operation, respectively. For example, responsive to each activation of the signal AREF, the RHR state control circuit 236 may provide a number of activations of the internal refresh signal IREF. Responsive to each activation of IREF (as long as the signal RHR is not active) an auto-refresh operation may be performed. The RHR state control circuit 236 may perform periodic targeted refresh operations by providing a number of activations of the signal RHR after counting a certain number of the activations of IREF. In other words, with timing based on AREF, the RHR state control circuit 236 may indicate that the memory should provide a first number of auto-refresh operations, then a second number of auto-refresh operations, then the first number of auto-refresh operations again, etc. For example, the RHR state control circuit 236 may indicate that 8 auto-refresh operations should be performed (e.g., by providing IREF eight times) and then may indicate that 4 targeted refresh operations should be performed (e.g., by providing IREF along with RHR four times), and then repeating that cycle for as long as the memory device is in a refresh mode. Other numbers of auto-refresh and targeted refresh operations may be used in other examples. Accordingly, a normal operation of the memory may include a period of time over which the memory performs some number of access operations (e.g., due to external commands) and then a period of time in a refresh mode (e.g., when AREF is being provided) where a sequence of auto- and targeted-refresh operations are being performed.

Responsive to receiving the signal RFM, the RHR state control circuit 236 may indicate that one or more panic targeted refresh operations should be performed. In some embodiments, after receiving the signal RFM, the RHR state control circuit 236 may perform a panic targeted refresh operation even if a refresh operation would not otherwise be performed. For example, after receiving the signal RFM, even if the memory device is not currently in a refresh mode, the refresh control circuit 216 may issue the signals IREF and RHR together to indicate that a targeted refresh operation should be performed. In some embodiments, access operations may be put ‘on hold’ while the memory performs a panic targeted refresh and access operations may then resume. In some embodiments, the RHR state control may indicate that multiple targeted refresh operations should be performed (e.g., by providing the signals RHR and IREF multiple times). For example, responsive to each activation of the signal RFM, the RHR state control circuit 236 may indicate that two panic targeted refresh operations should be performed. Other numbers of panic targeted refresh operations may be performed responsive to each activation of RFM in other examples.

The refresh control circuit 216 may include a skip logic circuit 239, which may receive the signals RFM and REF_IP and provide the signal Skip based on those two signals. The signal Skip may be used to indicate that the RHR state control circuit 236 should skip the next periodic targeted refresh operation (e.g., because enough targeted refreshes have already been performed by panic targeted refreshes before the current refresh mode). In some embodiments the signal Skip may cause the RHR state control circuit 236 to skip all of the periodic targeted refresh operations in a next refresh period (e.g., the next period of time where there is a refresh mode). In some embodiments, where the memory performs multiple targeted refresh operations periodically as part of each refresh period, the signal Skip may cause the RHR state control circuit 236 to skip only a portion of the periodic targeted refresh operations. For example, only one periodic targeted refresh operation may be skipped due to the activation of the signal Skip. Other numbers of periodic targeted refresh operations may be skipped in other example embodiments.

When the RHR state control circuit 236 receives the signal Skip, it may skip (e.g., not perform) a next periodic targeted refresh operation. In some embodiments, the RHR state control circuit 236 may skip a periodic targeted refresh operation by not performing any kind of refresh operation. In some embodiments, the RHR state control circuit 236 may skip a periodic targeted refresh operation by performing an auto-refresh operation instead (e.g., by providing the signal IREF alone). When a periodic targeted refresh operation is skipped, the RHR state control circuit 236 may provide an activation of a signal REF_IP which indicates that a periodic targeted refresh operation was skipped. The activation of REF_IP may be a pulse of the signal, where the signal is changed from an inactive level to an active level for a period of time, and then returned to the inactive level.

The skip logic circuit 239 may provide the signal Skip based on a count of the number of panic targeted refresh operations. The skip logic circuit 239 may count a number of activations of the signal RFM and compare that count to a threshold. For example, each time the signal RFM is activated, a count value N in the skip logic circuit 239 may be increased (e.g., incremented by one). Each time the count value N is changed, it may be compared to a threshold N_th. When the count value N meets or exceeds the threshold N_th, the signal Skip may be provided. The signal Skip may continue to be provided at an active level until the RHR state control circuit 236 responds to the signal Skip (e.g., by skipping a next periodic targeted refresh operation). Responsive to the RHR state control circuit 236 skipping a periodic targeted refresh operation (e.g., when the RHR state control circuit 236 provides the signal REF_IP), the skip logic circuit 239 may change the count N in a different direction than the value N is changed responsive to the signal RFM. For example, responsive to a periodic targeted refresh operation being skipped (e.g., responsive to the signal REF_IP), the count value N may be decreased. In some embodiments, the count value N may be decreased by the value of the threshold N_th. In some embodiments, the count value N may be reset to an initial value (e.g., 0).

The value of the threshold N_th may be based on a number of targeted refresh operations performed as part of each periodic targeted refresh cycle and a number of targeted refresh operations performed responsive to each activation of the signal RFM. For example, the value of the threshold N_th may be set as multiple of the ratio of the number of targeted refresh operations performed per periodic targeted refresh cycle (I) to the number of targeted refresh operations performed responsive to each activation of the signal RFM (J). In one example embodiment, the value of N_th may be given by N_th=2*I/J. The value of N_th may be programmable, for example it may be set by a trim fuse of the memory.

In some embodiments, the skip logic 239 may separately control skip operations for targeted refresh operations on different types of victim word lines. For example, the skip logic 239 may include a first threshold N_th1 and when the count N is above the threshold N_th1, the skip logic circuit 239 may provide a signal which causes a next periodic targeted refresh operation on +/−1 (e.g., adjacent) victim word lines to be skipped. The skip logic 239 may also include a second threshold N_th2 and when the count N is above the second threshold N_th2, the skip logic circuit 239 may provide a signal which causes a next periodic targeted refresh operation on a +/−2 victim word lines to be skipped.

FIGS. 3A-3B are timing diagrams of an operation of a refresh control circuit according to an embodiment of the present disclosure. The timing diagrams 300 a and 300 b show the operation of refresh control circuit (e.g., 116 of FIG. 1 and/or 216 of FIG. 2) which counts refresh management signals RFM in order to determine when to skip a next periodic targeted refresh operation. FIGS. 3A-3B show different embodiments of the operation of a skip logic circuit (e.g., 239 of FIG. 2). In particular, FIG. 3A shows an embodiment where after a periodic targeted refresh operation is skipped, the count value N is decreased by the threshold value N_th (which in the example of FIG. 3A is 2). For example, each time the signal REF_IP is provided, the count value N may be decreased by N_th. FIG. 3B shows an embodiment where after a periodic targeted refresh operation is skipped, the count value N is reset to an initial value (in this case, 0). For example, each time the signal REF_IP is provided, the value N may be reset to 0.

FIGS. 3A and 3B both show the same pattern of accesses to a memory bank. A first line of the timing diagrams 300 a-b shows the relative rate at which the memory bank is being accessed. Time may be represented along an x axis, starting from an initial time t0. A period of time labelled as a ‘heavy attack’ (e.g., t0 to t1, and t3 to t4) represents a period over which the memory bank is receiving a very high rate of access commands, which may signify that it is undergoing a malicious attack such as a row hammer attack. A period of time labelled as a ‘light attack’ (e.g., t1 to t2) represents a period over which the memory bank is receiving a high rate of access commands, which may be part of a malicious attack, however the rate of accesses during the light attack is less than the rate during the heavy attack. A period of time labelled ‘no attack’ (e.g., t4 to t5) indicates that the memory is receiving a normal rate of access commands.

The second line of the timing charts 300 a-b shows the refresh operations performed by the memory along with the refresh management signal RFM as well as the accesses between the refresh operations. For purposes of clarity, the timing diagrams of FIGS. 3A-3B show a simplified periodic refresh pattern where each refresh mode includes a single auto-refresh operation and the opportunity for a single targeted refresh operation. It should be understood that other numbers of refresh operations can be used in other example embodiments.

The third line of the timing charts 300 a-b shows the count value N in the skip logic circuit (e.g., 239 of FIG. 2). To highlight the behavior of how the count value N is changed when a periodic targeted refresh operation is skipped, the count value is only shown each time the memory performs the periodic auto- and targeted refresh operations. Each time the count value N is shown, it is shown as a pair of values, the value of the count N just before the periodic refresh operations are performed and right after the periodic refresh operations are shown. An arrow is shown pointing at the numbers to indicate times where the periodic targeted refresh operations are skipped.

At the initial time t0, the count value (not shown) may be at 0 after the periodic targeted refresh operation just after t0 is skipped. In the case of both the embodiments shown in FIGS. 3A and 3B, the threshold N_th is set to a value of two. After the time t2, there is a gap where memory operations are not shown before the time t3. Starting at t3, similar to the initial time t0, the count value is 0 after a targeted refresh operation just after t3 has been skipped.

FIG. 3A shows a timing diagram 300 a for an embodiment where each time a periodic targeted refresh operation is skipped, the count value N is decreased by the value of the threshold N_th, which in this example embodiment is 2. After t0, the signal RFM is issued two times, and then there is a periodic refresh operation. At that periodic refresh operation, the targeted refresh operation is skipped and the count N is reduced to 0. Then there are four more RFM signals and the count is increased to 4. When the next periodic targeted refresh operation is skipped, the count N is dropped to 2. There are then three more RFM signals which raise the count N to 5. After the next periodic targeted refresh operation (e.g., because N=5>=N_th=2) the count is reduced to 3.

In the embodiment of FIG. 3A, periodic targeted refresh operations may continue to be skipped even when RFM signals are not being issued. Jumping ahead to the time t4, when a period of no attacks begins, the count value N stands at 4 after a periodic targeted refresh operation is skipped. The signal RFM is not provided and so the count N stays at a value of 4 when the next periodic refresh operations begin. Since the value of the count N still meets or exceeds the value of the threshold N_th, the periodic targeted refresh operation is skipped. Accordingly, in the embodiment of FIG. 3A, periodic targeted refresh operations may still be skipped even when the access rate to the memory is low enough that the signal RFM is not being provided.

FIG. 3B shows an embodiment where the count value N is reset to a minimum value (e.g., 0) each time a periodic targeted refresh operation is skipped. Starting at the initial time t0, as may be seen after two activations of the signal RFM, the count value N is 2. After a periodic targeted refresh operation is skipped, the count value N is reset to 0. There are then four activations of the signal RFM, and so the count value is N. After a next periodic targeted refresh operation is skipped, the count value N is reset again to 0. Resetting the value of N may help to ensure that periodic targeted refresh operations are only skipped when the signal RFM is provided between periods of refresh operation (e.g., when the memory bank is receiving access commands at a high rate). As may be seen, in contrast to the embodiment of FIG. 3A, in the embodiment of FIG. 3B, no targeted refresh operations are skipped after the period with no attacks begins at the time t4.

FIG. 4 is a schematic diagram of a skip logic circuit according to an embodiment of the present disclosure. The skip logic circuit 400 may, in some embodiments, be included in the skip logic circuit 239 of FIG. 2. The example skip logic circuit 400 may exhibit the behaviors shown in the timing diagram 300 b of FIG. 3B, and may reset a count value N each time a periodic refresh operation is skipped.

The skip logic circuit 400 includes a counter circuit 444 which stores and manages the value of the count N. In the embodiment of FIG. 4, the counter circuit 444 also manages the comparison of the count N to the threshold N_th, which is set based on a signal tmifz from a trim fuse (e.g., as set in a fuse array of the memory device). In other embodiments a separate comparator circuit may be used. When the count value N meets or exceeds the threshold N_th, the counter circuit 444 provides the signal Flag at an active level (e.g., a high logical level). The signal Flag may continue to be provided at an active level until the count value N is below the threshold N_th (e.g., until after the count value is reset).

A clk terminal of the counter circuit 444 is coupled to the refresh management signal RFM. Each time an activation of the signal RFM is received (e.g., a rising edge of RFM), the counter circuit 444 may increment the value of N. The counter circuit 444 may compare the count value N to the threshold N_th each time the count value is changed. A reset terminal of the counter circuit is coupled to a reset signal rst_n. When the counter circuit 444 receives an activation of the signal rst_n (e.g., the signal rst_n at a low logical level), the count value N may be rest to an initial value (e.g., 0) . . . . In some embodiments, the threshold may be set by setting a maximum value that the count value N may have, and then setting the signal Flag to an active level when the count exceeds the maximum value (e.g., rolls over). Accordingly, the signal tmfz may be used to set a maximum value of N to N_th−1.

The reset signal rst_n may be based on the state of the signal Skip. The signal Skip may be coupled through a delay circuit 442 to an inverter circuit 443. Accordingly, at a first time, the signal skip may rise from a low logical level to a high logical level (e.g., when the count value N meets or exceeds the threshold N_th). At a second time which is after the first time, the signal rst_n may change from a high logical level to a low logical level. This in turn may cause the count value to reset, and the signal Flag to drop to a low logical level.

The skip logic circuit 400 includes a latch circuit 452, which may store and provide a value of the skip signal Skip. The latch circuit 452 may be used to ensure that the signal Skip remains at an active level (e.g., a high logical level) until after a next periodic targeted refresh operation is skipped. As shown in the circuit of the example of FIG. 4, the latch circuit 452 may include a cross coupled pair of NOR gates. A first NOR gate has a first input terminal coupled to the signal Flag, and a second input terminal coupled to the signal Skip. The first NOR gate has an input terminal coupled to a first input terminal of the second NOR gate, which has a second input terminal coupled to a falling edge detector of the signal REF_IP (as described herein). The output of the second NOR gate is the signal Skip. The latch circuit 452 has a data terminal coupled to the signal Flag. When the signal Flag is received at an active level, the signal Skip saved in the latch circuit 452 is set to an active level. The latch circuit 452 has a reset terminal which is coupled to the output of a NOR gate 450 (which provides a signal at a high logical level responsive to a falling edge of the signal REF_IP). When the signal on the reset terminal is received at a high logical level, the signal Skip is changed to a low logical level.

The skip logic circuit 400 receives the signal REF_IP, which indicates that a periodic targeted refresh operation has been skipped. The signal REF_IP is coupled to the reset terminal of the latch circuit 452 through an inverter 446, a delay circuit 448, and a NOR gate 450 which act as a falling edge detector for the signal REF_IP. One of the input terminals of the NOR gate 450 is coupled to the signal REF_IP. The other input terminal of the NOR gate 450 is coupled to the signal REF_IP through the inverter circuit 446 and the delay circuit 448. Accordingly, when the signal REF_IP falls from an active level to an inactive level (e.g., a high logical level to a low logical level), the NOR gate 450 may provide a signal at a high logical level, which may reset the latch circuit 452 so that the signal Skip is provided at a low logical level.

FIG. 5 is a timing diagram of a signals of a skip logic circuit according to an embodiment of the present disclosure. The signals shown in the timing diagram 500 may show an example of signals which may be used by a skip logic circuit such as the skip logic circuit 400 of FIG. 4 which resets a count N each time a periodic targeted refresh operation is skipped. The timing diagram 500 shows a variety of signals over time, with time extending along the x-axis from left to right. Each of the signals is shown as a separate trace, with a low logical level shown as a first level on the y-axis and a high logical level shown as a second level of the y-axis which is above the first level (except for the count value N, which is shown as a numerical value).

The first trace shows the refresh management signal RFM, which is provided by a controller of the memory based on a rate of accesses to the memory. The second trace shows the signal REF_IP, which is used to indicate that a periodic targeted refresh operation has been skipped. The third trace shows the count value N over time. The fourth trace shows the signal Flag, which may be provided by a counter circuit (e.g., 444 of FIG. 4). The fifth trace shows the signal Skip, which may be provided by the skip logic circuit (e.g., 239 of FIG. 2).

Before an initial time t0, the value of the count N is at 0, and the signals REF_IP, Flag, and Skip are all at a low logical level. At t0, an activation of the signal RFM is received. This may indicate that the controller has counted a certain number of access commands directed to the bank. Responsive to the activation of RFM (e.g., responsive to a rising edge of RFM), the count value N is increased by one to a value of one. At a first time t1, a second activation of the signal RFM is received. This may raise the value of N to two, which in this example embodiment is the threshold value N_th.

Since the value of N is now equal to or greater than N_th, the signal Flag is raised to a high logical level, which in turn raises the signal Skip to a high logical level. The signal skip rising to a high logical level may in turn reset the count value N to an initial value (e.g., 0). This may cause the signal Flag to drop to low logical level. The signal Skip may be provided to the RHR state control circuit to indicate that the next periodic targeted refresh operation should be skipped. At a second time t2, the signal REF_IP is provided to indicate that the memory device has performed periodic refresh operations, and that a periodic targeted refresh operation has been skipped. At a third time t3, responsive to a falling edge of the signal REF_IP, and the signal Flag no longer being at a high logical level, the signal Skip drops back to a low logical level.

FIG. 6 is a flow chart of a method of dynamic targeted refresh steals according to an embodiment of the present disclosure. The method 600 may be implemented by the device 100 of FIG. 1 in some example embodiments.

The method 600 may include block 610 which describes receiving a refresh management signal at a bank of a memory. The refresh management signals may be based on access commands to a particular bank of the memory. The access commands may be access commands associated with, for example, reading or writing data to/from one or more word lines of the bank. The access commands may be provided by a controller (e.g., interface 226 of FIG. 2). The memory bank may include an access period where the access commands are sent and received, and a refresh mode period, where one or more refresh operations are performed. A pattern of access periods and refresh modes may repeat.

The refresh management signal may be based on a first count responsive to the access commands and comparing the first count to a threshold. The controller may include the first count value (e.g., RAA). In some embodiments, each time the access command is provided to a particular bank of the memory, the first count value may be increased (e.g., increased by one). The first count value may be compared to a first threshold (e.g., RAAIMT) and may determine if the first count RAA is greater than or equal to the first threshold RAAIMT. The refresh management signal (e.g., RFM) may be provided when the count is greater than the first threshold.

Block 610 may be followed by block 620 which describes changing a count responsive to the refresh management signal and comparing the count to a threshold. The refresh control circuit may include a skip logic circuit (e.g., 239) which manages the count value (e.g., N). In some embodiments, responsive to each refresh management signal (e.g., RFM), the count value N may be increased. The count value may be compared to a threshold (e.g., N_th) to determine if the count value is greater than or equal to the second threshold N_th.

Block 620 may be followed by block 630, which describes periodically performing a targeted refresh operation on the memory bank. The memory bank may be put into a refresh mode, where periodic refresh operations are performed. An interface may put the memory bank into the refresh mode by providing a refresh signal (e.g., AREF). While performing refresh operations, some of the refresh operations may be auto-refresh operations and some may be targeted refresh operations. The memory bank may receive access commands for a period of time, then be in a refresh mode for a period of time, and then this may repeat.

Block 630 may be followed by block 640, which describes skipping a next of the periodic targeted refresh operations based on the comparison of the second count to the second threshold. In some embodiments, when the second count is greater than or equal to the second threshold, the next periodic targeted refresh operation may be skipped. In some embodiments, after the next periodic targeted refresh operation is skipped, the count value N may be decreased. For example, the count value N may be decreased by the threshold N_th. In another example, the count value N may be decreased by resetting the value of N to an initial value (e.g., 0).

Of course, it is to be appreciated that any one of the examples, embodiments or processes described herein may be combined with one or more other examples, embodiments and/or processes or be separated and/or performed amongst separate devices or device portions in accordance with the present systems, devices and methods.

Finally, the above-discussion is intended to be merely illustrative of the present system and should not be construed as limiting the appended claims to any particular embodiment or group of embodiments. Thus, while the present system has been described in particular detail with reference to exemplary embodiments, it should also be appreciated that numerous modifications and alternative embodiments may be devised by those having ordinary skill in the art without departing from the broader and intended spirit and scope of the present system as set forth in the claims that follow. Accordingly, the specification and drawings are to be regarded in an illustrative manner and are not intended to limit the scope of the appended claims. 

What is claimed is:
 1. An apparatus comprising: a memory bank configured to receive a refresh management signal, wherein the refresh management signal is provided based on a rate of access commands directed to the memory bank; a skip logic circuit configured to change a count value responsive to the refresh management signal and configured to provide a skip signal based on the count value; and a refresh state control circuit configured to periodically provide a targeted refresh signal while the memory bank is in a refresh mode, wherein the targeted refresh control circuit is further configured to skip providing a next targeted refresh signal responsive to the skip signal.
 2. An apparatus comprising: a memory bank configured to receive a refresh management signal; a skip logic circuit configured to change a count value responsive to the refresh management signal and configured to provide a skip signal based on the count value, wherein the skip logic circuit is configured to change the count value in a first direction responsive to the refresh management signal and configured to change the count value in a second direction opposite the first direction based on the next targeted refresh signal being skipped; and a refresh state control circuit configured to periodically provide a targeted refresh signal while the memory bank is in a refresh mode, wherein the targeted refresh control circuit is further configured to skip providing a next targeted refresh signal responsive to the skip signal.
 3. The apparatus of claim 1, wherein the skip logic circuit is configured to provide the skip signal based on a comparison of the count value to a threshold.
 4. An apparatus comprising: a memory bank configured to receive a refresh management signal; a skip logic circuit configured to change a count value responsive to the refresh management signal and configured to provide a skip signal based on the count value, wherein the skip logic circuit is configured to provide the skip signal based on a comparison of the count value to a threshold; and a refresh state control circuit configured to periodically provide a targeted refresh signal while the memory bank is in a refresh mode, wherein the targeted refresh control circuit is further configured to skip providing a next targeted refresh signal responsive to the skip signal, wherein the skip logic circuit is configured to increase the count value responsive to the refresh management signal and configured to decrease the count value by the threshold responsive to the next targeted refresh signal being skipped.
 5. The apparatus of claim 1, wherein the refresh state control circuit is configured to provide a pulse of a command signal responsive to skipping the next targeted refresh signal.
 6. An apparatus comprising: a memory bank configured to receive a refresh management signal; a skip logic circuit configured to change a count value responsive to the refresh management signal and configured to provide a skip signal based on the count value, wherein the skip logic circuit is configured to provide the skip signal based on a comparison of the count value to a threshold; and a refresh state control circuit configured to periodically provide a targeted refresh signal while the memory bank is in a refresh mode, wherein the refresh state control circuit is configured to provide a pulse of a command signal responsive to skipping the next targeted refresh signal, and wherein the skip logic circuit is configured to reset the count value to an initial value responsive to receiving the pulse of the command signal.
 7. An apparatus comprising: a memory bank configured to receive a refresh management signal; a skip logic circuit configured to change a count value responsive to the refresh management signal and configured to provide a skip signal based on the count value, wherein the skip logic circuit is configured to provide the skip signal based on a comparison of the count value to a threshold; and a refresh state control circuit configured to periodically provide a targeted refresh signal while the memory bank is in a refresh mode, wherein the refresh state control circuit is configured to provide a pulse of a command signal responsive to skipping the next targeted refresh signal, and wherein the skip logic circuit is configured to reset the count value responsive to a falling edge of the pulse of the command signal.
 8. An apparatus comprising: a bank of a memory device; an interface configured to provide access commands and refresh management signals to the bank; a refresh control circuit associated with the bank, wherein the refresh control circuit is configured to: periodically indicate that a first type of refresh operation and a second type of refresh operation should be performed when the bank is in a refresh mode; indicate the first type of refresh operation when the bank is not in the refresh mode based on the refresh management signal; and reduce a number of the first type of refresh operation during a next time the memory is in the refresh mode based on a number of times the first type of refresh operation was indicated when the bank was not in the refresh mode.
 9. The apparatus of claim 8, wherein the first type of refresh operation is a targeted refresh operation and wherein the second type of refresh operation is an auto-refresh operation.
 10. The apparatus of claim 9, further comprising an aggressor detector circuit configured to identify an aggressor wordline of the memory bank, wherein during the first type of refresh operation at least one victim wordlines associated with the aggressor wordline is refreshed.
 11. The apparatus of claim 8, further comprising: a skip logic circuit configured to provide a skip signal based on a comparison of a count of the activations of the refresh management signal to a threshold, wherein the refresh control circuit is configured to indicate the first type of refresh operation when the memory bank is not in the refresh mode responsive to each activation of the refresh management signal, and wherein the refresh control circuit is configured to reduce the number of the first type of refresh operation responsive to the skip signal.
 12. The apparatus of claim 11, wherein the refresh control circuit is configured to periodically indicate that the first type of refresh operation should be performed a first number of times during the refresh mode and indicate that the first type of refresh operation should be performed a second number of times responsive to each activation of the refresh management signal.
 13. The apparatus of claim 12, wherein the threshold is based on the first number and the second number.
 14. The apparatus of claim 8, wherein the refresh control circuit is configured to reduce the number of the first type of refresh operation by skipping one or more times the first type of refresh operation is indicated during the next time the memory is in the refresh mode.
 15. A method comprising: receiving a refresh management signal to a bank of a memory; changing a count responsive to the refresh management signal and comparing the count to a threshold; periodically performing a targeted refresh operation on the memory bank; skipping a next of the periodic targeted refresh operations based on the comparison of the count to the threshold; and increasing the count responsive to receiving the refresh management signal and decreasing the count responsive to skipping the next of the periodic targeted refresh operations.
 16. The method of claim 15, wherein decreasing the count responsive to skipping the next of the periodic targeted refresh operation comprises decreasing the count by a value of the threshold.
 17. The method of claim 15, wherein decreasing the count responsive to skipping the next of the periodic targeted refresh operation comprises resetting the count to an initial value.
 18. The method of claim 15, wherein periodically performing the targeted refresh operations is during a refresh mode of the bank and wherein the method further comprises performing a targeted refresh operation responsive to the refresh management signal when the bank is not in the refresh mode. 